FIG. 1 shows an example of a portable instrument of the prior art, in this case a wristwatch 1, fitted with an analogue display device 2, whereas FIG. 2 shows a watch of the prior art comprising a digital display device 4. For reasons of convenience, identical elements will be designated by the same reference numerals in the following description.
Display devices 2, 4 are protected from the external environment by a protective glass 6 made of synthetic or mineral glass or any other transparent material. This protective glass 6 is mounted on case 8 of the instrument such that its lower surface, which is opposite display device 2, 4, extends at a certain distance therefrom. As is clear from FIGS. 1 and 2, this method of mounting a protective glass on case 8 of a portable instrument is commonly used, whether the display device is of the analogue type 2, i.e. it comprises hands l0a, l0bmoving above a dial 12 or of the digital type 4, i.e. it comprises a liquid crystal display cell in which a liquid crystal film is trapped between two substrates, provided on their opposing faces with a set of electrodes defining at their intersections a series of switchable segments for displaying information.
The use of protective glass 6 thus involves making the time information displayed by the display device appear to the wearer of the watch as though from a certain distance below the lower surface of the glass which, in a way, is detrimental to the aesthetic appearance of the watch.
Moreover, it is known that because of multiple light reflections which appear on the protective glass and on the top substrate of the cell in the case of a watch fitted with a digital liquid crystal type display device, the viewing angle at which the wearer can observe the displayed information decreases proportionally with the increase in the distance between the lower surface of the glass and the display device. The wearer of the watch is thus obliged to bend his wrist so that the face of the dial takes a substantially perpendicular position to his line of vision if he wishes to limit the effects of multiple reflections and observe the information displayed without interference. The parasitic reflections returned towards the observer are also undesirable in that they affect the contrast of the elements being observed through the glass.
Moreover, in the case of watches or instruments fitted with liquid crystal display device provided with a polarizer on the top substrate, the effect of the latter is lost when the device is observed from too great a viewing angle typically greater than 45°, so that the unswitched display segments become visible, which is detrimental to the legibility of the displayed information.
Another conventional drawback of watches fitted with an analogue display device is that the wearer has to orient the watch dial face such that it is substantially perpendicular to his line of vision if he wishes to remove or limit parallax error upon reading the analogue display.
It is an object of the present invention to overcome the aforementioned drawbacks in addition to others by providing a portable instrument such as a watch for improving reading comfort of the information provided by the analogue or digital display device, whatever the angle at which the display device is observed by the wearer of the watch.
It is also an object of the present invention to provide a portable instrument such as a watch for displaying information with improved contrast.
It is also an object of the present invention to produce a portable instrument such as a watch having new and original aesthetic effects in a simple and inexpensive manner.